The present invention relates to a microwave subharmonic mixer device.
It is often necessary to transpose the frequency f.sub.S of a signal to another and so-called intermediate frequency f.sub.FI. The mixer devices supplied with a signal at frequency f.sub.S and with a signal at frequency f.sub.OL from a local oscillator, provide a signal at a fundamental frequency f.sub.FI =.vertline.f.sub.OL .+-.f.sub.S .vertline..
It is difficult or troublesome however to produce stable local microwave oscillator sources. Consequently, it is preferable to make use--for frequency transposition--of a mixer of the subharmonic type, for example comprising a frequency doubler and a conventional mixer, making it possible to utilise a local oscillator at half the frequency, which is easier to make. The principle of a subharmonic mixer of this kind has been described by different authors in articles such as "Harmonically pumped stripline down-converter" by Martin V. Schneider and William W. Snell published in IEEE Transactions on Microwave Theory and Techniques, pages 271-275, vol. MTT-23, No. 3, March 1975. This article describes a mixer formed on a dielectric substrate suspended within a rectangular waveguide and comprising two Schotty-barrier diodes which are shunt mounted with opposite polarities at the junction of two filters, a band-pass filter at the side of the incident signal f.sub.S and a low-pass filter at the side towards the input of the local oscillator f.sub.OL, at which the intermediate frequency output also occurs. Due to the method of decoupling between the local oscillator and the incident signal, and the technology applied, this mixer can only be used in systems with a narrow band limited by the qualities of the filtering operation and the losses present in the filters.